In present day recording devices and particularly in disc drives there is employed a plurality of recording discs on which data can be recorded in binary form. These discs are usually referred to as a disc pack and are stacked one above the other to be addressed by a plurality of heads in vertical alignment and positioned by a single actuator.
In one embodiment of disc drives used today, one head and one disc surface are dedicated to the generation of a position signal for the servo system. Usually a plurality of servo tracks are recorded in concentric circles on the servo disc surface and the servo head generates a signal responsive to the relative position of the head and each servo track. Thus if the servo head is aligned over a desired track and the other heads are aligned with the servo head, they also will be aligned over a corresponding track on the respective cooperating disc surfaces.
For interchangeability of the disc packs, the various tracks recorded on each of the disc surfaces must be closely aligned with the prerecorded servo track so that the readback of the data from each disc pack is possible on recorders other than the one in which the data was recorded. Thus the normal procedure for assuring that the heads are in alignment vertically is to place on the drive a disc pack having prerecorded and precisely positioned servo tracks on all of the disc surfaces. Such prerecorded disc packs are referred to as CE or Customer Engineer Packs and are commercially available with disc drives for use in aligning the heads. Thereafter the actuator is energized to position the servo head at a desired track. By reading the signals from the individual heads and feeding such signals to a readout means, usually a visual type such as a signal strength meter, it can be detected whether or not that particular head is in close alignment with the data track corresponding to the track the servo head is positioned over. Thereafter provision is made for adjusting the position of each head/arm assembly relative to the carriage and therefore relative to the servo head. By making the necessary adjustment on each head to maximize the signal, the heads are brought into alignment with the servo head.
However problems have developed which make the alignment procedure just described either very difficult to perform or make the results less than satisfactory. For instance, the presence of the technician around and in contact with the disc drive results in vibrations being transmitted throughout the mechanism thereby making the servo signal hard to read. In addition the various normal vibrations in the building in which the drive is located are sensed by both the servo head and the read/write heads causing the position signal to be modulated by all types of other signals and even more difficult to read. Also there are other forces being exerted on the positioning system such as the force of the electrical leads running to the head and the pressure of the technician's tools while making the necessary adjustments, which forces tend to move the servo system off track sufficiently such that alignment of the head to that position will not align the head directly over the track once the force is removed since the servo system head has been moved off track slightly during the adjustment by the force. Thus after such adjustment the servo head will return to a center position and in doing so will move the read/write heads somewhat off track.
It is thus the object of this invention to provide an improved method and apparatus for aligning the read/write heads relative to the servo system in a disc drive assembly.